The disclosure relates generally to a method for the laser-based machining of preferably sheet-like substrates and to a corresponding device and to the use of methods and devices for separating sheet-like substrates, such as for example semiconductor wafers, glass elements, . . . (in particular of brittle materials) into multiple parts (individually separating the wafers or glass elements). As further described in detail below, work is in this case performed using lasers, generally pulsed lasers, with a wavelength to which the materials are substantially transparent.
Devices and methods for severing such materials by means of a laser are already known from the prior art. On the one hand (for example DE 10 2011 000 768 A1), it is possible to use lasers which, by virtue of their wavelength or their power, are strongly absorbed by the material, or after the first interaction make the material strongly absorbent (heating with for example the generation of charge carriers; induced absorption), and can then ablate the material. This method has disadvantages in the case of many materials: for example impurities due to particle formation in the ablation; cut edges may have microcracks on account of the heat input; cut edges may have melt edges; the cutting gap is not uniform over the thickness of the material (has a different width at different depths; for example a wedge-shaped cutting notch). Since material has to be vaporized or liquefied, a high average laser power has to be provided.
On the other hand, there are known laser methods for severing brittle materials that function on the basis of a specifically directed, laser-induced crack formation. For example, there is a method from Jenoptik in which a trace on the surface is first strongly heated by the laser, and immediately thereafter this trace is cooled so quickly (for example by means of a water jet) that the thermal stresses thereby achieved lead to crack formation, which may be propagated through the thickness of the material (mechanical stress) in order to sever the material.
There are also methods in which a laser at the wavelength of which the material is largely transparent is used, so that a focal point can be produced in the interior of the material. The intensity of the laser must be so high that internal damage takes place at this internal focal point in the material of the irradiated substrate.
The last-mentioned methods have the disadvantage that the induced crack formation takes place in the form of a point at a specific depth, or on the surface, and so the full thickness of the material is only severed by way of an additional, mechanically and/or thermally induced crack propagation. Since cracks tend to spread unevenly, the separating surface is usually very rough and must often be re-worked. Moreover, the same process has to be applied a number of times at different depths. This in turn slows down the speed of the process by the corresponding multiple.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.